A submarine cable aging detection method based on combined calculation of capacitance and resistance

Abstract

The application relates to the technical field of submarine cable insulation aging monitoring, in particular to a submarine cable aging detection method based on combined calculation of capacitance and resistance. C x和 Resistance R x The combined diagnosis method constructs a three-dimensional coordinate system, takes the distance D from the origin to the fitting plane as a comprehensive evaluation index, and realizes accurate identification and positioning of the submarine cable aging degree. The application has the advantages of online implementation ability and high-precision positioning performance, high detection precision, strong anti-interference ability, and can realize early warning of the submarine cable aging state in a complex marine environment, and provides a new technical approach for state monitoring and fault warning of the submarine cable.

Description

Technical Field

[0001] This invention relates to the field of submarine cable insulation aging monitoring technology, specifically a submarine cable aging detection method based on joint calculation of capacitance and resistance. Background Technology

[0002] By the end of 2025, the global cumulative installed capacity of wind power had exceeded 1,350 gigawatts (GW), and offshore wind farms are advancing towards large-scale development in deep-sea areas. Due to the combined effects of longer transmission distances and the unique operating environment of the seabed, high-voltage transmission technology has gradually become the mainstream solution for transmitting offshore wind power. Submarine cables, as the core load-bearing component of this solution, directly affect the stability of the entire transmission system. Compared to traditional underground cables, the harsh operating environment, highly fluctuating operating conditions, and harmonic currents on the seabed not only significantly accelerate the aging and deterioration of the cable insulation but also greatly increase the risk of insulation failure.

[0003] Current research largely focuses on passive insulation aging detection after a fault occurs, making it difficult to achieve early warning and prediction before faults occur. Therefore, accurately identifying the insulation status of submarine cables and locating cable sections with insulation degradation is a crucial prerequisite for targeted maintenance and ensuring the safe operation of the system. Currently, the main technical approaches applicable to submarine cable aging monitoring include reflection methods and broadband impedance spectroscopy (BIS), but most of these technologies lack online monitoring capabilities. The reflection method utilizes the time difference between the traveling wave and the reflected signal from the aging section to achieve location; however, when applied to submarine cable systems, it faces technical challenges such as weak impedance changes and severe signal attenuation. While the detection accuracy of BIS is superior to traditional offline monitoring technologies, it still faces several developmental bottlenecks: First, there is still a lack of systematic theoretical analysis of broadband admittance spectrum, and the selection of frequency band parameters lacks scientific basis; Secondly, the equivalent impedance of the converter can interfere with the spectral characteristics, affecting the accuracy of the detection. Third, traditional algorithms are difficult to adapt to the actual working conditions of data loss and non-uniform sampling intervals during online monitoring, and there is an urgent need to develop new detection methods with stronger adaptability; Therefore, a submarine cable aging detection method based on joint calculation of capacitance and resistance is needed to improve the above problems. Summary of the Invention

[0004] In order to solve the technical problems of low accuracy, poor anti-interference ability, and difficulty in early warning of submarine cable insulation aging online monitoring, this invention provides an invention title to solve the above problems.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A method for detecting aging of submarine cables based on joint calculation of capacitance and resistance includes the following steps: S1: The sensing component structure is designed for the special structure of submarine cables, and magnetically shielded leakage current monitoring devices are designed according to the different structures of "single core" and "three core" submarine cables.

[0006] S2: Equivalent parameter analysis of transmission lines, establishing an equivalent model of the distributed parameter circuit of submarine cables, and deriving the mathematical relationship between the capacitance parameters and transmission characteristics of submarine cables.

[0007] S3: Bus capacitance status monitoring. A linear fitting method is used to estimate the transmission line capacitance parameters online, and the capacitance estimation results are obtained. C x .

[0008] S4: C x and R x The joint diagnosis adds resistance parameter Rx estimation to the capacitance estimation to construct a capacitance-resistance joint analysis model, and uses the distance D from the origin to the fitting plane as a comprehensive evaluation index of the degree of aging.

[0009] S5: Online monitoring and location result analysis, identifying the location of aging sections and assessing the severity of aging based on the joint diagnostic results.

[0010] As a preferred embodiment of the present invention, step S1 involves designing magnetically shielded leakage current monitoring structures for both single-core and three-core submarine cable structures, specifically including: For the 10kV voltage level "multi-core" submarine cable structure, a two-layer electromagnetic shielding ring structure is designed. The inner layer shields the large current, and the outer layer shields the external electromagnetic field. The inner diameter of the magnetic shielding ring is designed to be 55mm, the outer diameter is designed to be 75mm, and the interval is 20mm. Two acquisition boards with different directions are deployed in the interval. Two magnetic pads are set at the connection of the open structure to block the connection.

[0011] For single-core submarine cables with voltage levels above 110kV, a triangular layout is adopted to include the three single-core conductors of phases A, B, and C in a ring. The inner diameter of the magnetic shielding ring is designed to be 108mm, the spacing is designed to be 10mm, and the outer diameter is designed to be 118mm. Four acquisition boards with different directions are deployed in the spacing.

[0012] As a preferred embodiment of the present invention, the equivalent parameter analysis of the transmission line in step S2 specifically includes: establishing an equivalent model of the distributed parameter circuit of the submarine cable, where R, L, G, and C represent the resistance, inductance, conductance, and capacitance values ​​per unit length of the submarine cable, respectively; according to the submarine cable transmission line theory, the voltage U and current I at any position x satisfy the transmission line equation; introducing the reflection coefficient ρL to describe the parameter relationship between the starting end and the terminal end; and deriving the mathematical expression between the submarine cable capacitance parameter C and the transmission characteristics:

[0013] Where Y' is the reciprocal of the admittance Y, γ is the transmission coefficient, ω is the angular frequency, and L is the total length of the submarine cable.

[0014] As a preferred embodiment of the present invention, the bus capacitor status monitoring in step S3 specifically includes the following steps: S31: Compare the output current of the equivalent circuit of the transmission line with the threshold current. When the output current is less than the threshold current, issue a warning command.

[0015] S32: Detects the stability of the output voltage at the end of the equivalent circuit cable. When the difference between the output voltage at the end and the bus reference voltage is within the threshold safety range, a warning command is issued; otherwise, a termination command is issued.

[0016] S33: After issuing a warning command, record the measurement results of output voltage and current within a preset time window.

[0017] S34: Calculate the estimated capacitance of the aging section according to the capacitance estimation formula.

[0018] S35: Collect a set of variables, calculate discrete points, plot discrete data, and perform linear fitting within a specified monitoring period.

[0019] S36: Determine the intersection point of the fitted curve and the y-axis, calculate the specific value of the capacitance, and estimate the severity of capacitor aging.

[0020] S37: Obtain a set of long-term capacitance estimates. C x and drawing C x The curve changes over time, providing real-time aging assessment signals.

[0021] As a preferred embodiment of the present invention, the capacitance estimation formula in step S34 is specifically as follows: When there are aging sections in the submarine cable, the capacitance estimate is represented as a series of damped oscillation signals:

[0022] Where λ is the reflection coefficient related parameter, δ is the ratio of the transmission coefficient of the aged section to the non-aged section, and L1, L2, and L3 are the lengths of different sections.

[0023] As a preferred embodiment of the present invention, the resistance parameters in step S4 R x The estimation specifically includes: deriving the characteristic impedance based on the relationship between characteristic admittance and capacitance. Z The expression:

[0024] After squaring Z, we split it into real and imaginary parts, and derive the derivation based on the correspondence of the imaginary parts. R x Estimation formula: ; Where Im(Z²) is the imaginary part of Z².

[0025] As a preferred embodiment of the present invention, the construction of the capacitance-resistance joint analysis model in step S4 specifically includes: establishing a three-dimensional coordinate system, so as to... and R x As variables on the coordinate axes, the fitted plane equation is expressed as: in x c， x R These are the state variables for the submarine cable core and the return path, respectively. y c ，y R These are the admittance components of the return paths for the submarine cable core and the metal sheath, respectively.

[0026] As a preferred embodiment of the present invention, the distance D from the origin to the fitting plane is defined as a comprehensive evaluation index of the degree of capacitor aging. The formula for calculating D is: , in w 1. w 2. w 3 represent the frequency characteristic values ​​in the fitted curve. h For plane z Draw when any value is taken y R - x R The parameters of the curve, when D and initial distance D When the ratio of 0 to 0 approaches a preset threshold, it is determined that the capacitor of the branch bus will experience an aging failure.

[0027] As a preferred embodiment of the present invention, the online monitoring and positioning result analysis in step S5 specifically includes: determining the location of aging in the submarine cable section by analyzing the damped oscillation characteristic amplitude and frequency information in the capacitance estimate, with the positioning error of the aging section being less than 6.5%.

[0028] As a preferred embodiment of the present invention, it also includes a hardware and software collaborative monitoring system. The system includes a magnetically shielded sensing component, a data acquisition unit, a signal processing unit, and an aging diagnosis unit. The sensing component acquires electrical parameters of the submarine cable, the data acquisition unit performs analog-to-digital conversion on the electrical parameters, the signal processing unit filters and extracts features from the acquired data, and the aging diagnosis unit executes a capacitance-resistance joint calculation method to realize online monitoring and early warning of the aging status of the submarine cable.

[0029] Beneficial effects This invention establishes a mathematical coupling model between the equivalent capacitance and resistance of the submarine cable busbar and the location of the aging section of the submarine cable. It quantifies the influence of converter characteristics on spectral characteristics and designs a non-intrusive signal injection strategy that requires no additional hardware equipment. This enables online extraction of equivalent capacitance parameters under system operation. By tracking the evolution of the capacitor from the initial aging stage to the severe aging stage, the change process of submarine cable insulation aging can be understood. This solution combines online implementation capability with high-precision positioning performance, providing a new technical approach for submarine cable condition monitoring and fault early warning. Attached Figure Description

[0030] Figure 1 This is a flowchart of the online monitoring method for insulation aging of submarine cables.

[0031] Figure 2 This is the structural design diagram of the sensing component.

[0032] Figure 3 This is the equivalent circuit diagram of the distributed parameter circuit of a submarine cable.

[0033] Figure 4 It is the fitting plane for the combined diagnostic method of Cx and Rx.

[0034] Figure 5 These are the observed data and the fitted curve.

[0035] Figure 6 Positioning simulation results diagram. Detailed Implementation

[0036] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0037] Example: Please refer to Figure 1-6 The method for detecting submarine cable aging based on joint capacitance and resistance calculations, as shown, includes the following steps: S1. Design of sensing component structure specifically for the special structure of submarine cables: Leakage monitoring device structures were designed for both single-core and three-core submarine cables. Considering the spacing and interference issues of the single cores, the magnetic shielding ring was made into a clamp structure with appropriate space. The structural design is as follows: Figure 2 As shown, a suitable magnetic shielding layer can be designed so as not to affect the acquisition of electromagnetic signals or the transmission of signals through submarine cables.

[0038] 1) "Multi-core" structure: It is mainly composed of an internal ABC three-phase integrated multi-core conductor (mainly copper and aluminum as materials), an inner shielding layer (conductor shielding), a main insulation (cross-linked polyethylene), an outer shielding layer (insulation shielding), a metal sheath (alloy lead sheath), a sheath, an inner lining layer, an armor layer, and an outer sheath layer. It is designed with a two-layer electromagnetic shielding ring structure. The inner layer shields large currents, and the outer layer shields external electromagnetic fields. Generally, 10kV submarine cables belong to the "multi-core" structure. The diameter of the electromagnetic shielding ring is relatively large, with an inner diameter of 55mm and an outer diameter of 75mm, spaced 20mm apart. Two acquisition boards with different directions are deployed in the interval. The open structure connection is blocked by two magnetic pads, which helps to avoid magnetic leakage and improve the sampling accuracy of weak currents. 2) "Single-core" structure: This generally refers to submarine cables with voltage levels above 110kV. Each single conductor contains only one phase. When designing the magnetic shielding ring, all three single-core conductors of phases A, B, and C need to be included in the ring. This places high demands on the miniaturization of the shielding ring structure; otherwise, it will affect on-site installation. Generally, the design is carried out at the position with the smallest spacing between the three conductors (a triangular shape). The outer diameter of the single core is 90mm, the inner diameter is designed to be 108mm, the spacing is designed to be 10mm, and the outer diameter is designed to be 118mm to reduce the overall volume of the magnetic shielding ring. The spacing design of the "single-core" structure is narrower than that of the "multi-core" structure. Four acquisition boards in different directions are deployed in the spacing to improve the measurement accuracy due to the influence of space.

[0039] To ensure long-term operational stability, the magnetic shielding ring is coated with three layers of protective coating: the bottom layer is epoxy zinc-rich primer with a thickness of 50μm; the middle layer is epoxy micaceous iron oxide intermediate paint with a thickness of 100μm; and the top layer is polyurethane topcoat with a thickness of 60μm, which can withstand salt spray testing for more than 2000 hours.

[0040] S2. Equivalent parameter analysis of transmission lines; equivalent circuit diagram of submarine cable distributed parameters is shown below. Figure 3 As shown, R , L , G ,and C These represent the resistance, inductance, conductance, and capacitance values ​​per unit length of the submarine cable, respectively. According to submarine cable transmission line theory, at any position... x voltage at U and current I Satisfy the following formula: (1) Where γ is the transmission coefficient. Y Indicates admittance characteristics, f The transmission line frequency is represented by the following expression, where the relationship between the transmission parameters and the admittance is as follows: (2) The tested submarine cables vary in length, resulting in voltage drops along the cables and thus differences in output voltage between the starting and ending points. The relationship between admittance, capacitance, and frequency is as follows: (3) Assuming the total length of the submarine cable being measured is L Introducing the reflection coefficient , Related to the capacitance and resistance of the starting and ending terminals: (4) Based on equations (2) and (4), derive the transmission formula for the entire submarine cable: (5) Substituting formula (3) into formula (4) yields the following: (6) Y’ yes Y The reciprocal of the value. The capacitance parameters in the transmission circuit can be viewed as a damped oscillating signal sequence linearly determined by the total length and time axis. The relationship between the cable length and capacitance characteristics can capture the aging location. Aging cable segments typically exhibit an increase in dielectric constant, insulation conductivity, and capacitance, which reflects the essence of the location method. The following method is based on bus capacitance status monitoring to monitor the aging state.

[0041] S3. Bus capacitor status monitoring strategy, the specific steps are as follows: 1) Output current of the equivalent circuit of the transmission line I(x) With threshold current I leakComparison, when the output current I(x) less than the threshold current I leak At that time, issue an early warning command. I leak Set according to submarine cable dielectric loss standards or monitor historical cable fault data; 2) Detect the stability of the output voltage at the cable end of the equivalent circuit. When the output voltage at the end... U(x) Between and bus reference voltage U ref If the difference is within the threshold safety range, an early warning command is issued; otherwise, the early warning command is terminated. 3) After issuing the warning command, record the output voltage within a few milliseconds. U(x) and current I(x) The measurement results; 4) Capacitor C estimation C x The bus capacitor can be equivalent to a resistor and a capacitor in series, assuming L Section 1 is aging; calculate the capacitance of the aging section. C x It is estimated that the subscript 1 is used to distinguish the segment to which the quantity belongs: (7) Modeling is performed using the reflection coefficient relationship between two sections at the starting point of the measured section of the submarine cable: (8) set up The capacitance expression for a submarine cable containing aging sections is shown in the following formula: (9) Since the changes in electrical parameters after degradation are relatively small, δ is close to 1. For submarine cables with aging sections, the capacitance estimate can be interpreted as a series of damped oscillation signals. The oscillation frequency of these signals is proportional to the location of the aging section and the length of the entire submarine cable. By analyzing the amplitude and frequency information of the damped oscillation characteristics in the capacitance estimate, the location of aging in the submarine cable section can be determined. 5) Calculate the estimated results of the capacitor section according to equation (7), representing the variable parameter values ​​of slope change, voltage change, and curve area change; 6) Collect the variable set within the specified monitoring period (e.g., one week, one month, etc.) and calculate the discrete points. Plot the discrete data and obtain the linear fitting result of the capacitance estimation of the aging section according to formula (9); 7) Determine the fitted curve and y The intersection of the axes is used to calculate the specific value of the capacitance and estimate the severity of capacitor aging. 8) Obtain a set of long-term capacitance estimation results. Cx ,draw C x A curve that changes over time; real-time aging assessment signals are issued.

[0042] C x The aging index to be estimated is obtained using a linear fitting method. The output voltage and current values ​​are measured and calculated according to equation (9). C x It is estimated that, due to the DC and AC sides of the submarine cable, the output voltage and current values ​​are used... C x The estimation results are independent of power grid conditions; therefore, this method inherently possesses advantages such as high cost-effectiveness, high accuracy, non-invasiveness, and robustness. It eliminates the need for voltage and current measurements between each series of bus capacitors, avoiding expensive and invasive measurement units, and does not interrupt normal operation or require intrusive monitoring and control. C x The estimates are robust to environmental and power grid changes, but comparisons with actual aging conditions revealed that... R x Changes C x The estimation has a certain impact, which in turn affects the diagnosis of aging.

[0043] S4 C x and R x Combined diagnostic methods (such as) Figure 4 As shown in the figure, in the above analysis, only the equivalent capacitance parameter of the submarine cable bus capacitance was used. C x The equivalent series resistance parameter was not utilized. R x Furthermore, since the external length and status of each submarine cable branch are unknown, changes in the cable's operational status can affect the online monitoring results of the bus capacitance status. Therefore, further consideration is needed on how to mitigate the impact of the cable's status and fully utilize its advantages. R x This enables accurate online monitoring of the aging status of capacitors on multiple branch busbars.

[0044] C x The estimate is shown in step 3. Next, we will... R x To make an estimate, use equation (2) and C x Estimate the relevant items separately R x The characteristic impedance is obtained from the relationship between characteristic admittance and capacitance. Z The expression is as follows: (10) Calculate the square of Z by splitting the real and imaginary parts. R x : (11) The real part of Z, as measured, is Re( Z 2 The imaginary part is Im( Z 2 The correspondence of the imaginary part is expressed as: (12) Organized R x The estimation formula is: (13) Under aging conditions C x and R x Joint diagnosis of variation patterns, construction of a three-dimensional coordinate system: (14) x c， x R These are the state variables for the submarine cable core and the return path, respectively. y c ，y R Discrete observation data consisting of the admittance components of the return paths of the submarine cable core and the metallic sheath, respectively. x c， y c )and( x R， y R It can be calculated from historical data, such as Figure 5 As shown, these observational data (at each aging level) x c， y c It exhibits a linear distribution. y c - x c Slope of fitted curve I x The negative value, y Intersections on the axis represent As the capacitors of the submarine cable busbars age, C x This reduces the number of curves and shifts the fitted curve upwards. Similarly, Figure 5 The data shown in the figure are the observation data for these three cases. x R， y R )and( y R - x R Fitted curve. The slope of the curve represents... I x The negative value, y Intersections on the axis represent R x， As aging progresses... R x As the number increases, the fitted curve shifts upwards.

[0045] The distance from the origin to the plane is defined as D This serves as a comprehensive indicator for assessing the degree of capacitor aging. (Fitted curve) y C - x C Get the maximum frequency w 1 and minimum frequency value w 3. Calculate the minimum distance D 0 and the intersection frequency are obtained. w 2; According to the plane equation, D equal: (15) h For plane z Draw when any value is taken y R - x R Curve, when D and D When the ratio of 0 approaches the threshold, it is determined that the bus capacitor of that branch will experience an aging failure.

[0046] S5. Online monitoring and positioning result analysis, such as Figure 6 As shown, the current monitoring frequency used in the simulation results was set to 1kHz~46kHz, with a frequency interval of 5kHz. This test included 260 samples under different aging conditions. The aging section length range was set to 0.06 to 0.10l, with the corresponding aging section positions all located in the 0-0.90l range and intervals of 0.10l. The degree of aging was determined by the relative permittivity of the main insulation material, which was set to 1.2 to 1.5 times its original value. The simulation successfully obtained capacitance estimation information. Figure 6 The test results of the aging section at different locations are shown. Under four different aging degrees, different aging locations correspond to different leakage current changes, and the positioning error is less than 6.5%.

[0047] Three methods—the method of this invention, the traditional single-capacitance monitoring method, and the traditional insulation resistance testing method—were used for comparative testing simultaneously. The continuous monitoring period was 30 days, and each test was repeated 5 times, with the average value taken. The core test data, comparison results, and verification indicators are as follows:

[0048] By constructing a set of online real-time monitoring and efficient inspection and maintenance software and hardware system for submarine cables, the sensor module development process utilizes the monitoring of electrical parameters such as capacitance and resistance of the submarine cable to identify and diagnose aging characteristics. This can significantly reduce the maintenance and repair costs of submarine cables, improve maintenance and repair efficiency, and enhance the safety and reliability of submarine cable operation. At the same time, the software and hardware systems work together to improve the data of the submarine cable network, enhance data quality, improve the level of lean and intelligent management of submarine cables, and improve fault handling and emergency repair capabilities. This enables proactive maintenance to replace reactive repair, providing strong technical support for submarine cable construction, inspection, surveying, emergency repair, online monitoring and other maintenance and construction scenarios. Taking the Yantai Qiuchang I line 110kV single-core submarine cable as an example, the method of this invention was used to monitor for 30 days and successfully warned of three aging sections of different degrees. After on-site verification by maintenance personnel, the average accuracy rate of submarine cable defect judgment was verified to be over 95%.

Claims

1. A submarine cable aging detection method based on combined calculation of capacitance and resistance, characterized in that, Includes the following steps: S1: The sensing component structure is designed for the special structure of submarine cables, and magnetically shielded leakage current monitoring devices are designed according to the different structures of "single core" and "three core" submarine cables. S2: Equivalent parameter analysis of transmission lines, establishing an equivalent model of distributed parameter circuit of submarine cable, and deriving the mathematical relationship between submarine cable capacitance parameters and transmission characteristics; S3: Bus capacitance state monitoring, using linear fitting method to estimate the transmission line capacitance parameter on-line, to obtain the capacitance estimation result C x ; S4: C x and R x Joint diagnosis, based on the estimation of the capacitance, the resistance parameter Rx estimation is increased, and the capacitance-resistance joint analysis model is constructed. The distance D from the origin to the fitting plane is taken as the comprehensive evaluation index of the aging degree. S5: Online monitoring and location result analysis, identifying the location of aging sections and assessing the severity of aging based on the joint diagnostic results.

2. The submarine cable aging detection method based on combined calculation of capacitance and resistance according to claim 1, characterized in that: In step S1, magnetically shielded leakage current monitoring structures are designed for both "single-core" and "three-core" submarine cable structures, specifically including: For the 10kV voltage level "multi-core" submarine cable structure, a two-layer electromagnetic shielding ring structure is designed. The inner layer shields the large current, and the outer layer shields the external electromagnetic field. The inner diameter of the magnetic shielding ring is designed to be 55mm, the outer diameter is designed to be 75mm, and the interval is 20mm. Two acquisition boards with different directions are deployed in the interval. Two magnetic pads are set at the connection of the open structure to block it. For single-core submarine cables with voltage levels above 110kV, a triangular layout is adopted to include the three single-core conductors of phases A, B, and C in a ring. The inner diameter of the magnetic shielding ring is designed to be 108mm, the spacing is designed to be 10mm, and the outer diameter is designed to be 118mm. Four acquisition boards with different directions are deployed in the spacing.

3. The submarine cable aging detection method based on combined calculation of capacitance and resistance according to claim 1, characterized in that: The equivalent parameter analysis of the transmission line in step S2 specifically includes: establishing an equivalent model of the distributed parameter circuit of the submarine cable, where R, L, G, and C represent the resistance, inductance, conductance, and capacitance values ​​per unit length of the submarine cable, respectively. According to the submarine cable transmission line theory, the voltage U and current I at any position x satisfy the transmission line equation. The reflection coefficient ρL is introduced to describe the parameter relationship between the starting end and the terminal end, and the mathematical expression between the submarine cable capacitance parameter C and the transmission characteristics is derived. Where Y' is the reciprocal of the admittance Y, γ is the transmission coefficient, ω is the angular frequency, and L is the total length of the submarine cable.

4. The submarine cable aging detection method based on combined calculation of capacitance and resistance according to claim 1, characterized in that, The bus capacitor status monitoring in step S3 specifically includes the following steps: S31: Compare the output current of the equivalent circuit of the transmission line with the threshold current. When the output current is less than the threshold current, issue a warning command. S32: Detects the stability of the output voltage at the end of the equivalent circuit cable. When the difference between the output voltage at the end and the bus reference voltage is within the threshold safety range, a warning command is issued; otherwise, the command is terminated. S33: After issuing a warning command, record the measurement results of output voltage and current within a preset time window; S34: Calculate the estimated capacitance of the aging section according to the capacitance estimation formula; S35: Collect a set of variables, calculate discrete points, plot discrete data, and perform linear fitting within the specified monitoring period; S36: Determine the intersection of the fitted curve and the y-axis, calculate the specific value of the capacitance, and estimate the severity of capacitor aging; S37: Obtain a set of long-term running capacitance estimation results C x and plot C x a curve over time, real-time sending an aging assessment signal.

5. The submarine cable aging detection method based on combined calculation of capacitance and resistance according to claim 4, characterized in that, The capacitance estimation formula in step S34 is as follows: When there are aging sections in the submarine cable, the capacitance estimate is represented as a series of damped oscillation signals: Where λ is the reflection coefficient related parameter, δ is the ratio of the transmission coefficient of the aged section to the non-aged section, and L1, L2, and L3 are the lengths of different sections.

6. The submarine cable aging detection method based on joint capacitance and resistance calculation according to claim 1, characterized in that, The resistance parameter in the step S4 R x The estimating specifically comprises: deriving the characteristic impedance based on the characteristic admittance and the capacitance relationship Z table Expression: After squaring Z, we split it into real and imaginary parts, and derive the derivation based on the correspondence of the imaginary parts. R x Estimation formula: Where Im(Z²) is the imaginary part of Z².

7. The method for detecting submarine cable aging based on joint capacitance and resistance calculation according to claim 1, characterized in that: The step S4 of constructing the combined capacitance-resistance analysis model specifically comprises: establishing a three-dimensional coordinate system, so as to and R x As a variable on the coordinate axes, the fitted plane equation is expressed as: in x c， x R These are the state variables for the submarine cable core and the return path, respectively. y c ，y R These are the admittance components of the return paths for the submarine cable core and the metal sheath, respectively.

8. The submarine cable aging detection method based on joint capacitance and resistance calculation according to claim 7, characterized in that: The distance D from the origin to the fitting plane is defined as a comprehensive evaluation index of the degree of capacitor aging, and the calculation formula of D is: wherein w 1、 w 2、 w 3 are the frequency characteristic values in the fitted curve, respectively, h is the plane z draws y R - x R the parameters of the curve, when D the ratio of the initial distance D 0 to the preset threshold value, it is determined that the branch bus capacitor will fail due to aging.

9. The method for detecting submarine cable aging based on joint calculation of capacitance and resistance according to claim 1, characterized in that, The online monitoring and positioning result analysis in step S5 specifically includes: determining the location of aging in the submarine cable section by analyzing the damped oscillation characteristic amplitude and frequency information in the capacitance estimate, with the positioning error of the aging section being less than 6.5%.

10. The method for detecting submarine cable aging based on joint calculation of capacitance and resistance according to claim 1, characterized in that, It also includes a hardware and software collaborative monitoring system, which includes a magnetically shielded sensing component, a data acquisition unit, a signal processing unit, and an aging diagnosis unit. The sensing component collects electrical parameters of the submarine cable, the data acquisition unit performs analog-to-digital conversion on the electrical parameters, the signal processing unit filters and extracts features from the collected data, and the aging diagnosis unit executes a joint capacitance and resistance calculation method to realize online monitoring and early warning of the aging status of the submarine cable.

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